Many HIV-infected individuals in Kenya and other parts of sub-Saharan Africa are not aware of their status. Identifying these HIV-infected individuals and linking them to care and treatment is a critical part of improving their health and a cornerstone of HIV prevention. In the US, CDC guidelines support public health efforts to notify sex partners of persons newly diagnosed with HIV, and ensure that partners are tested and referred for medical care if infected. New data from a randomized clinical trial in Malawi have demonstrated the acceptability, feasibility and efficacy of offering partner notification services in an African setting. In collaboration with the Kenya Ministry of Health (MOH), we propose to introduce assisted partner notification services (aPS) into 18 facilities in Kenya and estimate its capacity to promote HIV testing, identify partners with HIV infection, and link these partners to care (Aim 1). We will use a cluster randomized clinical trial design with 9 clinics randomized to immediate aPS and 9 randomized to a 6-week delay in provision of aPS. Health providers in both arms will notify partners of the exposure to HIV without revealing information about the source, and partners consenting to HIV testing will be informed of their test result and referred for care if HIV- infected. Using outcome data from Aim 1, a cost-effectiveness analysis will be conducted to estimate the incremental cost per HIV-infected person identified and linked to care, and the incremental cost-effectiveness per incident HIV infection, HIV-related death, and disability adjusted life-year (DALY) averted in Kenya (Aim 2). The final aim focuses on collecting national data on reasons for HIV testing using a standardized Kenya MOH instrument to estimate the population level impact of aPS. By combining national surveillance data with information from Aims 1 and 2 on efficacy and cost-effectiveness, we will determine why some facilities are more successful than others and use this to improve program performance. These data will provide the rationale and information needed to move forward with scale-up of aPS in Kenya. Strong support from the HIV Prevention team at the National AIDS and STI Control Programme (NASCOP) makes this an achievable goal with potential to shift the face of the AIDS epidemic in Kenya.